Fall back to ANGLE on OpenGL 1.x

Apparently on some cards, that only provide OpenGL 1.4,
the check for OpenGL 2 specific functions is not sufficient
(presumably some old extensions provide the functions and so
the test passes, even though it really shouldn't)

To avoid crashing the apps later on, we should check the
context version and activate the fall back to ANGLE if it's
below 2.0.

Task-number: QTBUG-43870
Change-Id: Id0e3d8ad1f632334ba03bbb1a4802413f28436dc
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

src/plugins/platforms/windows/qwindowsopengltester.cpp

@@ -43,6 +43,7 @@
 #  include <QtCore/qt_windows.h>
 #  include <private/qsystemlibrary_p.h>
 #  include <d3d9.h>
+#  include <GL/gl.h>
 #endif
 
 QT_BEGIN_NAMESPACE
@@ -326,6 +327,37 @@ bool QWindowsOpenGLTester::testDesktopGL()
             goto cleanup;
 
         // Now that there is finally a context current, try doing something useful.
+
+        // Check the version. If we got 1.x then it's all hopeless and we can stop right here.
+        typedef const GLubyte * (APIENTRY * GetString_t)(GLenum name);
+        GetString_t GetString = reinterpret_cast<GetString_t>(::GetProcAddress(lib, "glGetString"));
+        if (GetString) {
+            const char *versionStr = (const char *) GetString(GL_VERSION);
+            if (versionStr) {
+                const QByteArray version(versionStr);
+                const int majorDot = version.indexOf('.');
+                if (majorDot != -1) {
+                    int minorDot = version.indexOf('.', majorDot + 1);
+                    if (minorDot == -1)
+                        minorDot = version.size();
+                    const int major = version.mid(0, majorDot).toInt();
+                    const int minor = version.mid(majorDot + 1, minorDot - majorDot - 1).toInt();
+                    qCDebug(lcQpaGl, "Basic wglCreateContext gives version %d.%d", major, minor);
+                    // Try to be as lenient as possible. Missing version, bogus values and
+                    // such are all accepted. The driver may still be functional. Only
+                    // check for known-bad cases, like versions "1.4.0 ...".
+                    if (major == 1) {
+                        result = false;
+                        qCDebug(lcQpaGl, "OpenGL version too low");
+                    }
+                }
+            }
+        } else {
+            result = false;
+            qCDebug(lcQpaGl, "OpenGL 1.x entry points not found");
+        }
+
+        // Check for a shader-specific function.
         if (WGL_GetProcAddress("glCreateShader")) {
             result = true;
             qCDebug(lcQpaGl, "OpenGL 2.0 entry points available");